'This is a problem for most high street supplement brands, as the majority are so poorly designed that they cannot be effective.'

Dr Clayton, who was advised the UK government's now defunct Committee on the Safety of Medicines in the 70s, added: 'They use untested, unproven and lowest-cost ingredients.

'Of all the vitamins, the multi-vitamins, omega 3, vitamin C tablets and the like, there is no evidence to support any of them.

'The one thing they all have in common is they don't work and have no evidence to support them. When you put any of these things to test, they don't do anything.'

'These products are being sold by companies who don't really know what they are selling, and being bought by customers don't really know what they're buying.

'But it doesn't really matter with nutritional supplements because they don't really do anything anyway – only to the consumer's wallet.'

Sales of supplements have grown by six per cent in five years, with Britons spending an estimated £442million on them in 2018, according to market research group Mintel.

Roughly 34 per cent of British people take health supplements daily, while the figure in the US is closer to the 50 per cent mark, according to a study published in JAMA.

This has been prompted by a health 'hype', with increasing numbers of people taking supplements, often endorsed by celebrities and influencers.

Dr Clayton, currently based in the US, predicts a transition from a 'dark age of pseudo-nutrition' to 'the age of evidence-based science'.

Dr Clayton said the supplement market is 'saturated'. But added there are scores of products with scientifically proven benefits, emerging.

These products, called nutraceuticals or 'super supplements', are not currently recognised as distinct from other supplements by officials.

Dr Clayton said: 'The growing consensus is that nutraceuticals are different from supplements because they have been tested and proven.'

The majority of food and dietary supplements in the US are regulated by the Food and Drug Administration agency, who can take dietary supplements off the market if they are found to be unsafe or if the claims on the products are 'false and misleading'.

In the UK, where supplements are monitored by the Food Standards Agency, as soon as products begin to make a medicinal claim, for example to prevent or treat disease, they must have a liscence under medicine legislation – the responsibility of The Medicines and Healthcare Products Regulatory Agency (MHRA).

But Dr Clayton, who is currently a fellow of the Institute of Food, Brain and Behaviour, a UK charity with Oxford University research programmes, said: 'The regulatory system was set up to protect the consumer from the nonsense sold on the high street, which I support.

'But it has not caught up with the new generation of nutritional science which has huge benefits.

'Many of the decisions are made for political reasons. Even if a nutraceutical produces medicinal benefits these cannot be publicised because, according to the law, only drugs are allowed to make such claims.

'The drugs industry is well aware of this, and uses it to protect its market. It needs to be updated and amended to bring new science.'

Dr Clayton is the director of science for LYMA, a brand that manufactures nutraceuticals.

The firm, based in the UK, uses patented ingredients, and has undergone extensive clinical tests to prove the products' efficiency and availability once digested - up to four times that of generic supplements.

Some people, including pregnant women, children below five years old and the elderly, are advised by professionals to supplement.

In response to Dr Clayton's views, UK supplement distributor Healthspan has said: 'We agree that many high street supplement brands are not effective. This is because they are not made to a pharmaceutical standard known as GMP.

'Healthspan products are made to GMP standard to ensure safety and consistency of dose. All herbs are checked to ensure they contain the correct plant extracts, and those with medicinal claims are licensed under THR legislation.'

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